01 - Preheat oven to 350°F. Grease and line three 8-inch round cake pans with parchment paper.
02 - In a large bowl, sift together flour, cocoa powder, sugar, baking powder, baking soda, and salt until thoroughly combined.
03 - In a separate bowl, whisk buttermilk, hot coffee, oil, eggs, and vanilla extract until smooth and well blended.
04 - Pour wet ingredients into dry mixture. Mix gently until just combined, being careful not to overmix the batter.
05 - Divide batter evenly among the three prepared pans. Smooth tops with an offset spatula for even baking.
06 - Bake for 30–35 minutes, or until a toothpick inserted into the center emerges clean.
07 - Let cakes cool in pans for 10 minutes, then invert onto wire racks to cool completely before frosting.
08 - Beat softened butter until creamy. Gradually add powdered sugar and cocoa powder on low speed. Mix in milk, vanilla, and salt. Beat until fluffy and spreadable, adding additional milk if necessary.
09 - Heat heavy cream in a small saucepan until just simmering. Pour over chopped chocolate and butter in a heatproof bowl. Let stand 2 minutes, then whisk until completely smooth. Allow to cool until thickened but still pourable.
10 - Place first cake layer on serving plate. Spread generous layer of frosting over top. Position second layer and frost again. Add third layer, then frost top and sides of entire cake.
11 - Pour prepared ganache over top of cake, allowing it to cascade down sides for dramatic effect.
12 - Refrigerate assembled cake for 20–30 minutes to set ganache before slicing and serving.